The objective of this program is to develop generic load models to simulate the composite load spectra (CLS) that are induced in space propulsion system components representative of the space shuttle main engines (SSME). These models are being developed through describing individual component loads with an appropriate mix of deterministic and state-of-the-art probabilistic models that are related to key generic variables. Combinations of the individual loads are used to synthesize the composite loads spectra. A second approach for developing the composite loads spectra load model simulation, the option portion of the contract will develop coupled models which combine the individual load models. Statistically varying coefficients of the physical models will be used to obtain the composite load spectra

Newell, J. F.

English

NASA Technical Reports Server

N87-22793
COMPOSIIE LOAD SPECTRA
FOR SELECT SPACE PROPULSION STRUCTURAL COMPONENIS*
J. F. Newell
Rocketdyne Division, Rockwell International
Canoga Park, California
The objective of this program is to develop generic load models to simulate
the composite load spectra (CLS) that are induced in space propulsion system
components representative of the space shuttle main engines (SSME). lhese
models are being developed through describing individual component loads with
an appropriate mix of deterministic and state-of-the-art probabilistic models
that are related to key generic variables. Combinations of the individual
loads are used to synthesize the composite loads spectra.
A second approach for developing the composite loads spectra load model
simulation, the option portion of the contract, will develop coupled models
which combine the individual load models. Statistically varying coefficients
of the physical models will be used to obtain the composite load spectra.
The need for this type of technology advancement is apparent from the demand
for higher performance, lighter weight, components that yield higher operating
pressures, temperatures, vibration and flow loads, Figure I. The difficulty
in installation, cost, and potential for new failure mechanisms limit the
required instrumentation to adequately define or verify loads. Proper
quantification of loads are required to minimize adding conservatism on
conservatism and to specify results so they can be accurately used for
structural analysis and risk assessment.
Rocketdyne is teamed with Battelle to develop this methodology. Rocketdyne is
using their background and expertise for the advancement in the loads
definition and analysis methods along with the extensive SSME test database
for comparitive information. Battelle is utilizing their expertise to develop
an advanced probabilistic code to represent the individual loads and load
spectra. Rocketdyne is packaging this total work in an easy to use expert
system type code. The following discussion covers an overview and
Rocketdyne's effort. Battelle's contribution is presented in a separate
report.
lhe CLS development is a 3-year base program with a 2-year option program.
The first 2 years of the base program have been completed. The effort has
three major tasks: probabilistic model theory and development, code
development and code validation and verification, Figure 2. Four classes of
rocket engine components are being used as examples for the load
development--turbine blades, transfer ducts, LOX posts and engine system
ducts, Figure 3 and 4. The available SSME instrumentation for use in
developing SSME related statistical data and load verification are also shown
in Figure 3.
*work performed under NASA Contract NAS3-24382
I15
I:II_CEOING PAGE BLM|K. NOT FILMEO
https://ntrs.nasa.gov/search.jsp?R=19870013360 2020-03-20T10:41:35+00:00Z
The probabilistic modeling requires simulation of the individual loads
summarized in Figure 5. Several shape simulations are required to
characterize these loads. The start and cutoff transients include a nominal,
random over nominal and spike load shape. The overall duty cycle required
to define engine operating conditions is represented as a nominal shape with a
random variation about the mean value. The basic nominal shapes of the duty
cycle operational requirements and inlet parameter operation bounds are
controlled by the engine contract requirements. These requirements are based
on vehicle thrust and operation needs, Figure 6. Environments like vibration
have a nominal variation dependent on a components power and/or speed, random
variation from hardware geometry and test to test conditions and transient
spikes from side loads, pops and chugs. The steady state dynamic loads are
represented in the frequency domain for both random and sinusoidal loads,
Figure 7.
Since the CLS methodology is to be applied to advanced engines, the loads are
being developed from a generic basis. The use of hardware specific random
variations like pump efficiency, head rise or flow resistance allow for engine
to engine load variations. Accounting for variations in power level, pump
speed, and engine inlet operating conditions allow for test to test variation,
Figure 8. The use of key variables and appropriate physical and probabilistic
models assures the methodology is applicable to variations in the SSME or to
new rocket engine designs. The results obtained from the loads spectra models
are being compared with available SSME engine measured results and available
analytical calculations.
The probabilistic loads model being developed by Battelle is implemented as
part of an expert system developed as part of the program. The expert system
is a tool to generate and analyze composite loads of a rocket engine design
and to supply these loads for use in either deterministic or probabilistic
finite element computer codes to perform structural analysis of engine
components. The probabilistic models are generic; the statistical information
utilized is primarily from the SSME test database. Expert opinion and other
engine background data are used where appropriate to complete the loads
picture.
The knowledge-based system manages the database, provides expert knowledge
relative to the generic probability loadings and generates the individual and
composite loads, Figure 9. The Battelle developed ANLOAD module performs the
probabilistic modeling and statistical analysis. A database system has been
developed to efficiently represent the knowledge. This database system
facilitates the communication between the expert system and the knowledge
base. The current knowledge base contains information for SSME type engines,
system type loads using the influence coefficient method, and local turbine
blade load scaling methods.
The expert system is a rule based system. The rules are modularized where
each module is designed to solve a particular problem or to perform a task.
The load expert system LDEXPI Version 2.0, Figure lO, has rule modules for
engine system dependent loads for all four components as well as selected
individual local component loads. The rules so far mostly relate to overall
process control and information retrieval, Figure II. The on-going rule
development is working on local individual load components and the more
complex composite load spectra. Knowledge for the transfer ducts is partially
developed and is being added to the system. The other two component loads are
being developed.
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Composite load spectra for select space propulsion structural components

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